The invention is directed to apparatus and methods for applying liquid materials to a web and further processing the web by application of additional liquid material to the web through an electrostatic field.
Conventional web-offset printing presses utilize heat-settable ink that is set or cured by heat after the ink is printed onto a paper web. The curing of the ink is typically done by passing the web through a dryer, which causes the temperature of the web to be raised to a relatively high temperature, such as in the range of 230xc2x0 to 320xc2x0 F. (Fahrenheit). After it passes from the dryer, the hot web must be cooled to allow effective processing of the web in subsequent operations.
FIG. 1 schematically illustrates a prior art web-offset printing press 10 of the type described generally above. Referring to FIG. 1, the prior art printing press 10 incorporates a plurality of rotatable printing cylinders 12, 14, each of which applies an image to a paper web 16 using a heat-settable ink. The paper web 16, which is guided by a number of rollers 18, passes through the printing press 10 from left to right, as indicated by the arrow shown in FIG. 1.
After the ink is applied by the printing cylinders 12, 14, the web 16 is passed through a dryer 20, which sets the ink by raising the temperature of the web 16 to a relatively high temperature. After passing through the dryer 20, the web 16 is passed over a plurality of chill rolls 22 to cool the web 16. Heat from the web 16 is absorbed by relatively cool water which is piped through the chill rolls 22. After passing through all of the chill rolls 22, the web 16 is at or close to (within 10xc2x0 F.) room temperature.
After being heated by the dryer 20 and cooled by the chill rolls 22, the paper web 16 has very little moisture content. Consequently, after being cooled by the chill rolls 22, the web 16 is fed to an electrostatic remoistener 24 which adds moisture back to the web 16. The remoistener 24 is provided with a plurality of spray nozzles (not shown) for spraying water droplets onto the paper web 16 and a plurality of field directors (not shown) on each side of the web 16 for generating a directed electrostatic field. The field directors on one side of the web 16 are maintained at a high voltage relative to the field directors on the other side of the web 16, and water is sprayed through the electrostatic field so that the water droplets travel within a confined path between the spray nozzles and the paper web 16.
In one aspect, the invention is directed to an apparatus for processing a moving web of material. The apparatus has an applicator that applies a liquid material to the moving web, a drying apparatus that heats the web to an initial temperature, a first cooling apparatus that causes the web to be cooled to a second temperature that is at least about 20xc2x0 F. lower than the initial temperature, and a second cooling apparatus disposed after the first cooling apparatus that causes the web to be cooled to a third temperature that is at least about 20xc2x0 F. lower than the second temperature. The first cooling apparatus includes a generator adapted to generate a directed electrostatic field through which the web passes and a sprayer adapted to spray liquid through the electrostatic field and onto the web.
The electrostatic field generator may include a plurality of first field directors disposed on a first side of the web, each of the first field directors having a plurality of electrodes, a plurality of second field directors disposed on a second side of the web opposite the first side, each of the second field directors having a plurality of electrodes, and a voltage supply that supplies a relatively high voltage to the electrodes of one of the first or second field directors.
The invention is also directed to a method of processing a moving web comprising the steps of: (a) applying a liquid material to the web, (b) heating the web to a first temperature, (c) generating a directed electrostatic field, (d) causing the web to pass through the directed electrostatic field, (e) spraying liquid through the electrostatic field and onto the web to cause the web to be cooled to a second temperature that is at least about 20xc2x0 F. lower than the first temperature, and (f) causing the web to be cooled to a third temperature that is at least about 20xc2x0 F. lower than the second temperature.
During step (a), the liquid material may be applied evenly to the web to create a substantially uniform coating of the liquid material on the web, or alternatively, during step (a) ink may be applied by a plurality of printing cylinders to generate a plurality of images on the web.
In another aspect, the invention is directed to an apparatus for processing a moving web. The apparatus is provided with an applicator that applies a liquid material to the web, a drying apparatus that heats the web to an initial temperature of at least about 200xc2x0 F., and an electrostatic cooling apparatus that causes the initial temperature of the web to be reduced to a lower temperature no greater than about 150xc2x0 F. without the use of any chill rolls. The electrostatic cooling apparatus includes a generator adapted to generate a directed electrostatic field through which the web passes and a sprayer adapted to spray liquid through the electrostatic field and onto the web.
The invention is also directed to a method of processing and cooling a web exclusively with an electrostatic cooling apparatus and without the use of a chill roll. The method includes the steps of: (a) applying a liquid material to the web, (b) heating the web after the liquid material has been applied to cause the web to have a temperature of at least about 200xc2x0 F., (c) generating a directed electrostatic field, (d) causing the web to pass through the directed electrostatic field when the web has a temperature of at least about 200xc2x0 F., and (e) spraying liquid through the directed electrostatic field and onto the web to cause the web to be cooled to a reduced temperature of not greater than about 150xc2x0 F. In accordance with the method, the cooling of the web is caused exclusively by an electrostatic cooling apparatus having a sprayer and an electrostatic field generator and not by a chill roll.
In the above apparatus and method, the liquid material may be applied evenly to the web to create a substantially uniform coating of the liquid material on the web, or alternatively, ink may be applied by a plurality of printing cylinders to generate a plurality of images on the web.
The features and advantages of the present invention will be apparent to those of ordinary skill in the art in view of the detailed description of the preferred embodiment, which is made with reference to the drawings, a brief description of which is provided below.